The Research On The Modification Of Meta-aramid Fibrid And Its Reinforcement Of PTMG/TDI-based Polyurethane Elastomers

Polytetramethylene ether glycol/toluene diisocyanate（PTMEG/TDI）-based polyurethane elastomer has high hardness,high resilience,low heat generation,hydrolysis resistance,excellent adhesion performance,flex fatigue resistance and low hysteresis loss,and is widely used in dynamic fields,such as roller skate wheels and various casters.However,it shows insufficient mechanical properties and wear resistance in high load areas,such as large sand conveying pipe linings,polyurethane truck tires,and rubber rollers for papermaking.So it is necessary to add reinforcing fillers to improve the comprehensive performance of the elastomer.Meta-aramid fibrid（MAF）has a unique ribbon structure with a large specific surface area,more surface active groups and at the same time,possesses long-lasting thermal stability,excellent flame retardancy,outstanding chemical stability,excellent mechanical properties of meta-aramid fiber.Therefore,this paper introduces MAF as a reinforcement material into PTMG/TDI-based polyurethane elastomers,and explores the chemical modification treatment method of MAF and its effect on the properties of composites.First,MAF was modified by high-temperature phosphorylation to obtain phosphoric acid-modified MAF（MAFP）.FTIR characterization revealed that-POH was introduced into MAFP.MAFP/PU composites were prepared,the process performance and mechanical performance tests found that the mechanical properties of MAFP/PU and the prepolymer processing fluidity were improved,but the improvement was limited.Therefore sodium dichloroisocyanurate（DCCNa）was used to modify MAF to obtain chlorinated MAF（MAFC）.The mechanism of chlorination modification was explored using FTIR and XPS.As a result,it was found that active groups such as amino（-NH₂）,carboxyl（-COOH）,and chlorine were introduced after MAFC was chlorinated.The contact angle test proved that the surface energy of MAFC increased from 21.9 m J/m² to 49.1m J/m² after chlorination modification,and the contact angle with PU prepolymer decreased from 70.9°to 30.7°indicating that the interfacial wettability of the MAFC and the PU matrix has been significantly improved.Secondly,the effect of the type of chain extender on the performance of PTMG/TDI-based polyurethane elastomers was studied.It was found that 3,3′-dichloro-4,4′-diaminodiphenylmethane（MOCA）chain-extended elastomers have the higher mechanical properties and microphase separation.A series of MAFC/PU with different MAFC contents were prepared by in-situ polymerization.FTIR results found that MAFC/PU was successfully prepared,and the effect of MAFC on the internal structure of PU was analyzed from the perspective of micro-phase separation;The mechanical performance results show that when the filler content is 1.5wt%,the tensile strength and tear strength of MAFC/PU（PU-FC-1.5）are36.1 MPa and 80.1 k N·m^-1,respectively,which are 43.3%and 21.2%higher than pure PU,respectively.The mechanical properties are better that of MAFP/PU;SEM found that MAFC showed a stretched band shape in PU-FC-1.5 which etched the PU matrix,and PU remained on the surface,indicating that the interfacial adhesion with the matrix was better;TG test results show that compared with pure PU,T_im of PU-FC-1.5 is increased by 10.1℃,T_5%is increased by 12℃,heat resistance is significantly improved;DSC found that compared with pure PU,the T_m,h of PU-FC-1.5 was improved to 15.9℃,which has excellent heat resistance performance;DMA results show that the tanδof PU-FC-1.5 is similar to pure PU,maintaining the low heat generation performance of the matrix;The processing performance results show that the prepolymer viscosity of PU-FC-1.5 at 80℃curing processing temperature reaches 4.3Pa·s,which is not conducive to processing and molding,and the processing fluidity needs to be further improved.Thirdly,in order to further improve the processing fluidity and mechanical properties of the composites,a two-component polyurethane coating agent was made to modify the MAFC to obtain the polyurethane-coated MAFC（PMAFC）.The mechanical properties and SEM tests found that the best coating solution concentration of PMAFC is 7.5 wt%and the best reinforced size is 18-20 mesh.Finally,PMAFC/PU composites were prepared by in-situ polymerization method and pre-polymerized post-addition method,and it was found that the composites prepared by in-situ polymerization had better mechanical properties.Therefore,a series of PMAFC/PU composites with different PMAFC content were prepared by in-situ polymerization using PMAFC with the optimal 7.5%coating agent concentration and 18-20 mesh reinforced size.The mechanical properties test results found that when the filler content is 1.5wt%,the tensile strength and tear strength of PMAFC/PU（PU-PFC-1.5）reached 40.9 MPa and 87.1 k N·m^-1,which were 61%and 31.8%higher than pure PU,respectively,and further improved compared to MAFC/PU;After the process performance test,it was found that the viscosity of PU-PFC-1.5 prepolymer was only 2.6 Pa·s at 80℃curing processing temperature,and the processing fluidity was better;DMA results found that the E′,E′′and tanδof PU-PFC-1 and PU-PFC-1.5 are slightly higher than that of pure PU,which is because the coating modification makes more chemical cross-linked structure between PMAFC and polyurethane matrix,but the overall composites still maintains good low heat generation performance;The flex test found that with the addition of PMAFC,the fatigue resistance of PTMG/TDI-based polyurethane elastomer was significantly improved,and the service life was improved;The tests of rolling wear resistance and sand resistance water abrasion performance found that the abrasion quantityΔm gradually decreased with the increase of filler content.Compared with pure PU,the rolling wear performance and the sand water resistance of PU-PFC-2 were improved by 59.6%and 44.6%,respectively.In summary,the comprehensive performance of PMAFC/PU composites was improved and has certain application value.